The Yellow-tailed Woolly Monkey is endemic to the montane rain forests and cloud forests of the Departments of San Martín (eastern part) and Amazonas (western part) in the Peruvian Andes, south and east of the Río Marañón, at altitudes of 1,400 to 2,700 m above sea level. Shanee et al. (2007) reported that it may still also occur in small areas of Cajamarca, Huanuco, Loreto and La Libertad departments (Mittermeier 1975; Graves and O?Neil 1980; Leo Luna 1980, 1982, 1989; Parker and Barkley 1981), but according to DeLuycker and Heymann (2007) they are now restricted to irregular, scattered parts of only two Departments: Amazonas and San Martín.